Gas generating device with initiator insulating means



23, 1966 J. R. CRAIG ETAL 3,267,672

GAS GENERATING DEVICE WITH INITIATOR INSULATING MEANS Filed Dec. 17, 1964 i 39 3 Fig. l

James R. Craig Daniel J. Sasmo BY W a. W

A lforney United States Patent 3,267,672 GAS GENERATING DEVICE WlTH INITIATOR INSULATING MEANS James R. Craig and Daniel J. Sasmor, Albuquerque, N. Mex, assignors, by mesne assignments, to the United States of America as represented by the United States Atomic Energy (Zommission Filed Dec. 17, 1964, Ser. No. 419,258 6 Claims. (Cl. 60--39.47)

The present invention relates generally to gas generators employing solid propellant or gas generating charges and more particularly to providing such gas generators with means to inhibit current flow through the propellant combustion initiating means subsequent to actuation thereof.

Gas generators are often utilized to provide a source of high pressure combustion products in response to an operating condition of the system or systems in which the gas generators are used. For example, a gas generator may be used in a system in which a signal from an accelerometer or other environmental or condition responsive device couples a self-contained power supply to the gas generator initiator upon attainment of a predetermined operating condition. Such a gas generator, particularly when utilizing bridgewires in the propellant combustion initiator, i.e., the ignition assembly, suffers shortcomings or drawbacks in that during combustion of the gas generating charge the housing and the ignition assembly are subjected to the abrasive turbulent action of the burning gas generating charge so as to cause particles of conductive metals, e.g., iron, chromium, nickel, etc., to be eroded from the housing and ignition assembly. These conductive particles deposit across the bridgewire contact surface area and, in effect, re-establish the circuit formerly provided by the bridgewire, thus causing a short or low resistance of about Ohms or lower so as to short circuit the power supply, which may be detrimental since the power supply may also be employed for initiating or operating some other device.

The present invention aims to overcome or substantially minimize the above and other shortcomings or drawbacks by utilizing in the combustion chamber of the gas generator a layer or lining of an electrically insulating substance that is disposed around the solid propellant in close contiguity to the inner wall of the gas generator housing, such that during propellant burning the erosion of the insulating substance causes portions of the substance to be deposited across the bridgewire contact surface and thereby provide a high resistance coating to inhibit current flow between the bridgewire contacts. That is, the noted objectionable re-est-ablishment of the initial circuit is thereby overcome. Aluminum, preferably anodized, in the closely contiguous lining relationship provides a highly satisfactory combustion chamber liner since aluminum oxide is a good electrical insulator and is compatible with the propellant as to prevent objectionable reaction therebetween.

The aluminum oxide is used in the form of a layer against the inner wall of the gas generator housing since in this relationship the aluminum layer does not appreciably form a fuel component which would be burned up during the combustion of the solid propellant, thus providing little, if any, coating material for the contacts.

An object of the present invention is to provide a new and improved solid propellant gas generator of compact construction.

Another object of the present invention is to provide means in a solid propellant gas generator for preventing the formation of objectionable low resistance coatings across igniter contacts during and subsequent to the burning of the solid propellant.

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A further object of the present invention is .to effect the deposition of electrical insulating material across the igniter contacts in a gas generator during combustion.

Other and further objects of the invention will be obvious upon an understanding of the illustrative embodiment about to be described, or will be indicated in the appended claims, and various advantages not referred to herein will occur to one skilled in the art upon employment of the invention in practice.

A preferred embodiment of the invention has been chosen for purposes of illustration and description. The preferred embodiment illustrated is not intended to be exhaustive nor to limit the invention to the precise form disclosed. It is chosen and described in order to best explain the principles of the invention and their application in practical use to thereby enable others skilled in the art to best utilize the invention in various embodiments and modifications as are best adapted to the particular use contemplated.

In the accompanying drawings:

FIG. 1 is a sectional view showing a solid propellant gas generator embodying the present invention;

FIG. 2 is a fragmentary plan view of a bridgewir initiator used to ignite a solid propellant charge; and

FIG. 3 is a fragmentary plan view showing a bridgewire initiator as in FIG. 2 after combustion of a solid propellant in a gas generator incorporating the present invention.

The gas generator assembly 10 shown in FIG. 1 may comprise a housing or casing 12 which is preferably made of high strength metal such as stainless steel or the like because of the high pressures encountered during combustion and since such metal provides a means of achieving overall compactness of a gas generator without sacrificing strength. The housing 12 is shown as generally bell shaped with an opening at one end thereof that may incorporate a ring or closure member 14 for defining a combustion chamber 15 within the housing. The closure member 14 may be provided with a peripherally extending threaded surface 16 and be secured to the housing by providing the latter with a threaded surface 17 which may be radially outwardly offset from the inner wall 20 of the housing defining the combustion chamber 15. The closure member 14 may be provided with a centrally disposed combustion products discharge port which may be in the form of a converging nozzle 22, as shown, or in the form of a De Laval type reaction nozzle (not shown) having a converging-diverging configuration.

The combustion chamber 15 may be loaded with a high energy, rapid burning solid propellant or gas generating charge 23, the details of which will be discussed in greater detail below.

The head or the closed end of the housing 12 may be provided with a centrally disposed passageway 24 with the walls thereof threaded to receive and retain an initiator or igniter assembly generally indicated at 25. This igniter assembly may comprise a generally T-shaped tubular support member 27 having a stern portion 28 and a flange portion 29. The stem portion may be provided with a threaded section to engage the threaded walls of the passageway 24 and thereby draw the flange portion 29 of the support member against the inner wall 20 of the housing. Another section of the stem portion may project from the housing 12 and be provided with means such as pins 30, for receiving and retaining a mating connector component (not shown). A suitable annular sealing ring 31 such as a silicon O-ring or the like may be disposed in an annular groove 32 in the flange portion 29 to provide a seal between the housing and igniter assembly.

A plurality of electrical contact pins or leads 35 may be disposed in the passageway through the support mem ber and be of such length as to be disposed intermediate the ends of the support member 27. These leads 35 may be oriented and insulatively spaced from each other by placing in the support member passageway at a location laterally inwardly from the flange portion 29 of the support member a first dielectric body 37 of a rigid dielectric material such as glass which may be afiixed to the metal support member in any suitable manner. A second dielectric body 38 of a suitable material, such as hard rubber, epoxy resin and the like, may be disposed in the support member passageway at a location laterally inwardly from the threaded section of the stem portion as to be in an abutting relationship with the glass dielectric. This second dielectric body 38 may preferably be formed in place and be of such length as to leave a portion of the leads 35 exposed to facilitate connection of the leads to an external power source. The passageway through the support member may be provided with an inwardly projecting shoulder 39 to aid in the positioning and retention of the dielectric bodies.

A portion of the glass body 37 in registry with the combustion chamber 15 may be machined or otherwise cut away to provide a cup-shaped pocket or cavity 41 of a diameter less than that of the glass body 37 as to form the socket walls from an annular segment of the glass body. The leads 35 terminate within the pocket 41 adjacent the innermost surface thereof to provide exposed spaced apart mounting terminals or contacts for a pair of bridgewires 43 and 44 which, as shown in FIG. 2, extend between four of the six exposed terminals. These bridgewires, which may be welded, soldered, or otherwise secured to the leads 35, are preferably disposed in close proximity to the innermost glass surface and comprise any suitable bridgewire material in wire form such as Nichrome, platinum, and the like, or they may comprise vapor deposited strips, printed connectors, carbon connectors, or other suitable bridging material.

As shown in FIGS. 2 and 3, there are six leads 35 in the igniter assembly with four of the leads providing contacts or terminals for the two bridgewires 43 and 44 while the other two leads may be interconnected by the coupling 42 within the dielectric body 38 to provide a continuity loop for facilitating circuit checking.

Ignition of the propellant charge 23 may be initiated by using a primary ignition composition 45 in the pocket 41 and a secondary ignition composition 46 in a tubular container 48 which may be secured to the support member 27 by providing the latter with an annular tang 49 which may be bent over a flange 51 on the container to hold the latter in place. The container 48 may be made of any suitable frangible or readily destructible material which is compatible with the propellant charge, such as, for example, nylon or the like. Also, the primary and secondary ignition compositions may be separated from each other by a thin film 47 of suitable material such as Mylar or the like.

Disposed within the combustion chamber 15 in close proximity to or against the inner wall 20 of the housing in the liner 50 of aluminum which provides a novel feature of the present invention. This liner of aluminum is preferably initially anodized to provide it with a thick coating of aluminum oxide (A1 rather than using an aluminum liner with only a thin surface film of naturally oxidized aluminum. Using the anodized aluminum liner over the non-anodized aluminum liner is desirable in that the coating of aluminum oxide provided by the anodizing is initially in the form of an electrical insulator, whereas, with the non-anodized aluminum liner there must first be a reaction with the oxygen produced during the burning of the solid propellant to provide the aluminum oxide necessary to form the desired insulating material. This reaction, i.e., 4Al+3O +2Al O is not only time consuming but requires the use of oxygen developed during the burning of the solid propellant that is normal- 1y used for the combustion of the fuel components in the solid propellant.

The aluminum liner may be formed in any suitable manner such as by die-pressing or the like to attain an unbroken configuration. After the liner is formed in its desired shape it may be anodized by placing it in a warm sulfuric acid solution and subjecting the solution to an electrical current.

The combustion chamber liner is preferably of a configuration similar to that of the inner wall 20 of the housing so that it may be disposed in a contiguous relationship with the inner wall 20. The portion of the liner covering the inner wall adjacent the igniter assembly may be provided with an opening therethrough of a diameter slightly greater than that of the flange portion 29 of the igniter assembly so that the lining terminates in a contiguous relationship with the peripheral surface of the flange portion. However, if desired the liner may extend radially inwardly a greater distance such as to lie intermediate the housing and the flange portion of the support member. The other or opposite end of the aluminum liner may terminate at a location adjacent the threaded oflset surface 17.

While the aluminum liner 50 may, after being formed, be loosely placed in the combustion chamber 15, it is preferable to use suitable bonding material such as a resin or the like between the housing and the aluminum liner 50 as indicated at 52.

The aluminum liner 50 is preferably of a sufficient thickness that it remains intact throughout the combustion of the solid propellant with only the surface portion of the liner which is exposed to the interior of the combustion chamber being eroded away. Part of the liner material that is eroded away is deposited in the pocket 41 as to provide a coating of high resistance material across the contacts as shown in FIG. 3. Also, while a relatively thick liner 50 is preferable, a thinner aluminum foil may be used; but since the foil is thinner it may be substantially removed from the inner wall of the housing during combustion such that the housing becomes exposed during the later stages of propellant burning.

The novel construction of the gas generator 10 lends itself to compactness in that, for example, the overall dimensions of the generator may be about four inches in length and about three inches in diameter. With a gas generator having these dimensions or even larger or smaller dimensions the thickness of the liner 50 may be about .013 to .017 of an inch The solid propellant charge and the igniter compositions may be of any suitable type. For example, in a gas generator the solid propellant charge may comprise a nitrocellulose composition, the primary ignition composition may comprise lead styphnate, and the secondary ignition composition 46 may comprise pelletized boron potassium nitrate. This particular charge is capable of producing about 50,000 ft.-lbs. of energy.

The solid propellant charge may be loaded into the housing until it attains a level comm-on with or slightly above the end of the secondary ignition composition container 48. After loading the housing with the propellant charge a frangible disc 54 of a suitable material such as stainless steel of about .005 of an inch in thickness, may be placed across the combustion chamber discharge opening and held in place by the end closure.

In operation of the gas generator hereinbefore described a suitable signal from an accelerometer or other environmental or condition sensing mechanism (not shown) effects the coupling of a self-contained power source, which may be a battery, capacitor or any other suitable means, shown diagrammatically at 56 to the igniter assembly 25 for actuating the primary ignition composition 45 by rapidly heating either one or both the bridgewires 43 and 44 until it or they are destroyed or broken. The firing of the composition 45 ignites the secondary composition which, in turn, ignites the solid propellant charge 23 to provide high pressure combustion products for operating or otherwise affecting a suitable gas actuated device or system (not shown).

It has been found that in order to prevent the shorting of the power supply 56 there should be a resistance across the contacts 3 5 of at least 150 ohms within about 100 milliseconds for a period of at least 2 seconds after initiation of the igniter with a constantly applied voltage of volts. When using a gas generator without the aluminum oxide liner of the present invention the resistance across the contacts is usually less than 150 ohms and frequently less than 50 ohms within 100 milliseconds. However, with gas generators incorporating the aluminum oxide liner the resistance at and beyond 100 milliseconds after initiation is normally over one megohrn with the foil liner and with the gas generators incorporating the preferred form of the aluminum liner the resistance is at least 5,000 ohms to about 94,000 ohms.

While the aluminum oxide liner provides a substantial portion of the insulating coating across the contacts 35, other conductive materials from the gas generator are also deposited across the contacts. However, these deposited conductive materials are of insufficient quantity when combined with the aluminum oxide to establish a low resistance current path across the contacts particularly since the aluminum liner protects the housing from being eroded by the burning propellant. Even when us ing the thinner aluminum foil, a higher resistance coating is obtained since substantially the entire foil is eroded away with a substantial portion of the foil being deposited across the contacts prior to the erosion of the housing.

It will be seen that the present invention sets forth a new and improved gas generator utilizing bridgewire ignition means. Also, the invention affords a novel combustion chamber liner -for inhibiting current drain from a power supply during and subsequent to the burning of the solid propellant.

As various changes may be made in the form, construction and arrangement of the parts herein Without departing from the spirit and scope of the invention and without sacrificing any of its advantages, it is to be understood that all matter herein is to be interpreted as illustrative and not in a limiting sense.

We claim:

1. A gas generating device of the character described comprising in combination a housing having an inner Wall and a closed end and :an open end defining a combustion chamber, a liner of aluminum metal disposed in close contiguity to the inner Wall of said housing to isolate said inner wall from the combustion chamber, ignition means including electrical leads penetrating said housing and extending into said combustion chamber, a bridgewire coupling at least one of said electrical leads with said bridgewire being destroyed upon application of an electrical current to said leads, and an ignitable gas generating charge within said combustion chamber and liner to provide gas and the essentially simultaneous erosion of said liner to efiect deposition of liner portions on said ignition means.

2. A gas generating system as claimed in claim 1 wherein said aluminum liner is provided with an electrically insulating aluminum oxide coating, and said coat.- ing is subjected to said erosion to effect deposition of aluminum oxide onto said ignition means.

3. A gas generating system claimed in claim 1 wherein a self-contained power source is coupled to said bridge- Wire for providing said electrical current, the circuit flow of said electrical current is interrupted upon destroying said bridgewire and maintained essentially interrupted by the said deposition of the liner.

4. A gas generating system as claimed in claim 1 wherein said aluminum liner is about .015 of an inch in thickness and is bonded to said inner wall.

5. A gas generating device of the character described comprising in combination a housing having an inner wall and a closed end and an open end defining a combustion chamber, a liner of aluminum metal disposed in close contiguity to the inner wall of said housing to isolate said inner wall from the combustion chamber, ignition means penetrating said housing and extending into said combustion chamber and comprising a support member with a rigid dielectric disposed therein and electrical leads, said dielectric having a cavity in an end thereof in registry with the combustion chamber with said electrical leads terminating within said cavity, a bridgewire coupling at least one of said electrical leads with said bridge- Wire being destroyed upon application of an electrical current to said leads, and an ignitable gas generating charge within said combustion chamber and liner to prov vide gas and the essentially simultaneous erosion of said liner to eiiect deposition of liner portions on said ignition means.

6. A gas generating system as claimed in claim 5 wherein a tubular container is affixed to said support member and projects essentially through said gas generating charge, and an ignition composition is in said tubular container for igniting said gas generating charge after being ignited by said ignition means.

References Cited by the Examiner UNITED STATES PATENTS 2,953,720 9/1960 Engel.

2,980,021 4/1961 Adelman -3982 2,987,880 6/1961 Kimmel 6035.6 3,083,610 4/1963 Lancy 6035.6 3,173,367 3/1965 Shinpaugh l0270.2 X

OTHER REFERENCES Rocket Refractories, by H. B. Porter, Navord Report 4893, Nots 1191, August 1955, pages 1, 2, 3, 9, 23 and 24.

MARK NEWMAN, Primary Examiner.

CARLTON R. CROYLE, Examiner. 

1. A GAS GENERATING DEVICE OF THE CHARACTER DESCRIBED COMPRISING IN COMBINATION A HOUSING HAVING AN INNER WALL AND A CLOSED END AND AN OPEN END DEFINING A COMBUSTION CHAMBER, A LINER OF ALUMINUM METAL DISPOSED IN CLOSE CONTIGUITY TO THE INNER WALL OF SAID HOUSING TO ISOLATE SAID INNER WALL FROM THE COMBUSTION CHAMBER, IGNITION MEANS INCLUDING ELECTRICAL LEADS PENETRATING SAID HOUSING AND EXTENDING INTO SAID COMBUSTION CHAMBER, A BRIDGEWIRE COUPLING AT LEAST ONE OF SAID ELECTRICAL LEADS 